The subject of this invention is a free fall submersible life saving device, particularly for offshore structures working in extremely heavy weather conditions.
The life saving appliances generally used on board offshore structures, including ships, are life boats and pneumatic life rafts. From Whittaker Survival Systems Bulletins 21C - 483, 36/38C - 483, 50/54 LR-483 and 50/54C - 483, however, life saving capsules and corresponding launching gear are also known. The launching gear permits fast lowering of the capsule by means of steel cables and winches. The design of these capsules is similar to the design of a well-known, enclosed life boat. The capsule is made of glass reinforced plastic. Inside the capsule, which is of ellipsoidal shape, can be seated 14 to 54 survivors, depending on the version of the capsule. The survivors are placed on a single-tier bench along the sides, bow and stern of the capsule, secured by safety belts. The capsule is self propelled. It also is fitted with a water spray installation for maintaining a fire barrier and with sanitary and radiolocation installations. It contains all necessary provisions of oxygen and food.
From a paper "Offshore Evacuation", published in "Safety at Sea", another life boat, in this case of the Norwegian makers Harding A/S, is known. It can be dropped from a height of 30 m. The hull structure is made of steel. The life boat is placed on inclined rails and kept in position by hook with its bow pointing to the surface of the water. The bow is very slender to produce relatively low forces when the life boat is dropped into the water; after the hooks are released, the life boat accelerates rapidly so that it submerges under the water surface. After a few seconds, it emerges and sails away from the danger are using her own power. Airplane chairs are provided for the survivors. The back rests of these chairs point in the direction of the deceleration of the forces created by the life boat striking the water surface.
Evacuation of the survivors is facilitated by two-level platforms, each fitted on the level of entrance hatches to the boat. The survivors are secured to the chairs by special safety belts. Each boat can accommodate about 70 people. It is fitted with all the standard equipment, required by regulations and regional requirements, for propulsion, oxygen, food, sanitary arrangements, radiolocation, etc.
From Polish Patent No. 106757, there is known a device for underwater research, which contains a crew cabin made of glass-reinforced plastic. This cabin is distinguished by its construction. It is built of twelve pentagonal sandwich sections made of glass reinforced polyester or epoxy resin. Manholes and view ports are fitted in these pentagonal sections, which form a spherical structure capable of withstanding the outside water pressure. The edges of the pentagonal sections are made in the form of flanges pointing inwards. These flanges are glued together and the butts are reinforced additionally by laminate straps. Manhole and viewport openings are made in a manner similar to the sides of pentagonal sections.
The essential shortcomings of the above, as life-saving appliances, are the long times needed for getting them into readiness and lowering into the sea, as well as the production of high deceleration forces introduced by the free fall. They also strike the sea in close proximity to the offshore structure in danger. As the result of this, they are often damaged, and frequently destroyed when washed against the structure in heavy weather. Also, they do not isolate the survivors from external conditions, especially from the influence of waves. The impact of waves and wind upon the floating life saving appliance also causes drift, often for large distances from the place of casualty. As the result, search must be conducted over large areas, which decreases survival.
None of the above, as life-saving appliances, therefore, secures full safety, especially in extremely heavy weather conditions and in case of fire and gas. Casualty statistics show that many of these appliances could not be launched due to excessive heel of the offshore structure or that they were seriously damaged by striking against the structure or upon falling into the water. The problem of appliances releasing themselves without crew involvement and the time to evacuate the survivors therefore still remains open.